Cooling fin structure

ABSTRACT

A cooling fin structure used in a cooler for an electric device includes a plurality of pin fins ( 71 ) arranged in a zigzag form in a coolant passage ( 80 ). Each of the pin fins ( 71 ) has a circular portion ( 72 ) having a circular cross-section, and irregularly shaped portions ( 73 ) provided contiguously on the upstream and downstream sides of the circular portion ( 72 ) as viewed in a direction of flow of the coolant. The irregularly shaped portions ( 73 ) have an outer peripheral surface ( 75 ) that is formed along a circumference ( 130 ) having a center at a center point ( 101 ) of the circular portion ( 72 ) of a pin fin ( 71,   71 B) that is located adjacent to the pin fin ( 71, 71 A) having the irregularly shaped portions ( 73 ), in an oblique direction relative to the direction of flow of the coolant.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to a cooling fin structure, and moreparticularly to a structure of cooling fins arranged in a zigzag form.

2. Description of the Related Art

A cooling fin device that aims at improving the cooling efficiency ofcooling fins of a heat sink provided in an electronic device isdisclosed in Japanese Patent Application Publication No. 2002-185175 (JP2002-185175 A). In the cooling fin device disclosed in this publication,the cooling fins are discretely placed like pin-type fins, and have astreamline shape relative to the direction of flow of cooling water.

Also, a cooling device for a semiconductor device as disclosed inJapanese Patent Application Publication No. 2003-324173 (JP 2003-324173A) aims at efficiently dissipating heat while reducing a pressure lossin a coolant channel. In the cooling device for the semiconductor deviceas disclosed in this publication, protruding elements shaped like finsare formed such that the length or height of the protruding elements ismaximized in a region corresponding to substantially the center of thesemiconductor device, and the length of the protruding elementsgradually decreases toward the outer side. Each of the protrudingelements has a spindle shape in a transverse cross-section.

As disclosed in the above-identified publications, coolers in which pinfins are placed on a coolant passage are used for cooling various typesof electronic devices that generate heat. As typical arrangements of thepin fins, the pin fins may be arranged in the form of a matrix, or thepin fins may be arranged in a zigzag form.

Where the pin fins are arranged in a zigzag form, the coolant passesthrough clearances between pin fins arranged in a row, and is thenconfronted with another row of pin fins present ahead of the coolant.Therefore, the coolant proceeds while winding toward the opposite sidesrelative to the direction of flow of the coolant. In this case, thepressure loss in the flow of the coolant that flows in the coolantpassage is increased, as compared with the arrangement of pin fins in amatrix form through which the coolant proceeds almost straight. Theincrease in the pressure loss in the flow of the coolant may result inincrease of a load on a motor for supplying the coolant, and reductionof the cooling efficiency with which the electronic device is cooled. Inorder to improve the cooling efficiency of the electronic device, it isnecessary to efficiently transfer heat from the pin fins to the coolant,as well as reducing the pressure loss in the flow of the coolant.

SUMMARY OF THE INVENTION

The invention provides a cooling fin structure used in a cooler in whichpin fins are arranged in a zigzag form, wherein a pressure loss in theflow of a coolant is reduced, while the efficiency of heat transfer fromthe pin fins to the coolant is improved.

A cooling fin structure according to one aspect of the invention is usedin a cooler for an electronic device. The cooling fin structure includesa plurality of pin fins arranged in a zigzag form in a coolant passagethrough which a coolant flows. Each of the pin fins has a circularportion having a circular cross-section, and irregularly shaped portionsprovided contiguously on the upstream side and downstream side of thecircular portion as viewed in a direction of flow of the coolant. Theirregularly shaped portions have an outer peripheral surface that isformed along a circumference having a center at a center point of thecircular portion of an adjacent one of the pin fins that is locatedadjacent to the pin fin having the irregularly shaped portions, in anoblique direction relative to the direction of flow of the coolant.

With the cooling fin structure constructed as described above, each ofthe pin fins is provided with the irregularly shaped portions, wherebythe surface area of the pin fin that contacts the coolant, and thecross-sectional area of the pin fin, are increased, as compared with apin fin that consists solely of a circular portion. As a result, theefficiency with which heat is transferred from the pin fins to thecoolant can be improved. Also, the outer peripheral surface of theirregularly shaped portions is shaped along a circumference having acenter at a center point of a circular portion of a pin fin locatedadjacent to the pin fin having the above irregularly shaped portions, inan oblique direction relative to the direction of flow of the coolant.With this configuration, the coolant smoothly flows between the pinfins, and vortex is less likely or unlikely to be generated at thedownstream side of the pin fins in the direction of flow of the coolant.Consequently, a pressure loss in the flow of the coolant can be reduced.

In the cooling fin structure according to the above aspect of theinvention, when a first pitch between the pin fins located adjacent toeach other in an oblique direction relative to the direction of flow ofthe coolant, as measured in a direction orthogonal to the direction offlow of the coolant, is equal to R+1/2×CL, and a second pitch betweenthe pin fins located adjacent to each other in the oblique direction, asmeasured in the direction of flow of the coolant, is equal to3^(t/2)(R+1/2×CL), where R is a radius of the circular portion, and CLis a clearance between the pin fins located adjacent to each other inthe direction orthogonal to the direction of flow of the coolant, theouter peripheral surface may be shaped along a circumference having aradius of R+CL.

With the cooling fin structure constructed as described above, it ispossible to increase the surface area of each pin fin that contacts withthe coolant and the cross-sectional area of the pin fin, while keepingthe width of the coolant passage formed between the pin fins locatedadjacent to each other in the oblique direction relative to thedirection of flow of the coolant, equal to the above-indicated CLdetermined in view of clogging of the coolant passage.

In the cooling fin structure according to the above aspect of theinvention, each of the irregularly shaped portions may have oppositecurved faces formed on opposite sides of a centerline that passesthrough the center point of the circular portion, contiguously withouter peripheral surfaces of the circular portion, each of the oppositecurved faces being provided by the outer peripheral surface formed alongthe circumference.

In the cooling fin structure according to the above aspect of theinvention, the irregularly shaped portions of each of the pin fins mayinclude an upstream end point located at an upstream end of the pin finhaving the irregularly shaped portions, as viewed in the direction offlow of the coolant, and a downstream end point located at a downstreamend of the pin fin as viewed in the direction of flow of the coolant.The pin fins located adjacent to each other in an oblique directionrelative to the direction of flow of the coolant may be positioned suchthat the downstream end point of the irregularly shaped portions of thepin fin located on the upstream side is located downstream of theupstream end point of the irregularly shaped portions of the pin finlocated on the downstream side, as viewed in the direction of flow ofthe coolant.

In the cooling fin structure according to the above aspect of theinvention, the irregularly shaped portion located on the upstream sideof the circular portion and the irregularly shaped portion located onthe downstream side of the circular portion may be symmetric withrespect to the center point of the circular portion.

A cooling fin structure according to another aspect of the invention isused in a cooler for an electronic device. The cooling fin structureincludes a plurality of pin fins arranged in a zigzag form in a coolantpassage through which a coolant flows. Each of the pin fins has acircular portion having a circular cross-section, and irregularly shapedportions provided contiguously on the upstream side and downstream sideof the circular portion as viewed in a direction of flow of the coolant.Each of the irregularly shaped portions is formed with outer peripheralsurfaces that are curved into a concave shape as viewed from a centerpoint of the circular portion, at opposite sides of a straight line thatpasses through the center point of the circular portion in the directionof flow of the coolant.

With the cooling fin structure constructed as described above, each ofthe pin fins is provided with the irregularly shaped portions, wherebythe surface area of the pin fin that contacts the coolant, and thecross-sectional area of the pin fin, are increased, as compared with apin fin that consists solely of a circular portion. As a result, theefficiency with which heat is transferred from the pin fins to thecoolant can be improved. Also, the outer peripheral surfaces of eachirregularly shaped portion are curved into a concave shape as viewedfrom the center point of the circular portion, at the opposite sides ofthe straight line that passes through the center point of the circularportion in the direction of flow of the coolant. With thisconfiguration, the coolant passage is formed between the pin finslocated adjacent to each other in an oblique direction relative to thedirection of flow of the coolant, along a path of the coolant thatproceeds while winding between the pin fins arranged in a zigzag form.Consequently, the coolant flows smoothly, and the pressure loss in theflow of the coolant can be reduced.

In the cooling fin structure according to the above aspect of theinvention, the irregularly shaped portions of each of the pin fins mayinclude an upstream end point located at an upstream end of the pin finhaving the irregularly shaped portions, as viewed in the direction offlow of the coolant, and a downstream end point located at a downstreamend of the pin fin as viewed in the direction of flow of the coolant.The pin fins located adjacent to each other in an oblique directionrelative to the direction of flow of the coolant may be positioned suchthat the downstream end point of the irregularly shaped portions of thepin fin located on the upstream side is located downstream of theupstream end point of the irregularly shaped portions of the pin finlocated on the downstream side, as viewed in the direction of flow ofthe coolant.

With the cooling fin structure constructed as described above, thesurface area of each pin fin that contacts the coolant, and thecross-sectional area of the pin fin, can be further increased. Also, thelength of the coolant passage formed between the pin fins locatedadjacent to each other in an oblique direction relative to the directionof flow of the coolant is increased. Therefore, the efficiency of heattransfer from the pin fins to the coolant can be more effectivelyimproved, and the pressure loss in the flow of the coolant can be moreeffectively reduced.

In the cooling fin structure according to the above aspect of theinvention, the irregularly shaped portion located on the upstream sideof the circular portion and the irregularly shaped portion located onthe downstream side of the circular portion may be symmetric withrespect to the center point of the circular portion.

In the cooling fin structure according to the above aspect of theinvention, the irregularly shaped portions of each of the pin fins mayinclude an upstream end point located at an upstream end of the pin finhaving the irregularly shaped portions, as viewed in the direction offlow of the coolant, and a downstream end point located at a downstreamend of the pin fin as viewed in the direction of flow of the coolant.The outer peripheral surfaces of each of the irregularly shaped portionsmay intersect with each other at an acute angle at the upstream endpoint and the downstream end point.

As explained above, according to the invention, the cooling finstructure in which the pressure loss in the flow of the coolant isreduced while the efficiency of heat transfer from the pin fins to thecoolant is improved can be provided in the cooler in which the pin finsare arranged in a zigzag form.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of anexemplary embodiment of the invention will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a circuit diagram showing the configuration of a systemconcerning motor-generator control of a hybrid vehicle;

FIG. 2 is a side elevation view showing a cooler for a power controlunit in which a cooling fin structure according to one embodiment of theinvention is used;

FIG. 3 is a cross-sectional view of the cooler for the power controlunit shown in FIG. 2, when viewed in a plane containing the X axis andthe Y axis;

FIG. 4 is a cross-sectional view showing, in enlargement, a part of thecooler for the power control unit shown in FIG. 3;

FIG. 5 is a graph comparing the equivalent coefficient of heat transferfrom pin fins to cooling water in the cooling fin structure of theembodiment of the invention, with that of a comparative example; and

FIG. 6 is a graph comparing a pressure loss in the flow of cooling waterin the cooling fin structure of the embodiment of the invention, withthat of the comparative example.

DETAILED DESCRIPTION OF EMBODIMENTS

One embodiment of the invention will be described with reference to thedrawings. In the drawings that will be referred to in the followingdescription, the same reference numerals are assigned to the same orcorresponding members or elements.

FIG. 1 is a circuit diagram showing the configuration of a systemconcerning motor-generator control of a hybrid vehicle. A cooling finstructure according to one embodiment of the invention is used in acooler for a power control unit (PCT) installed on the hybrid vehicle.Referring to FIG. 1, the motor-generator control of the hybrid vehiclewill be described.

The hybrid vehicle uses an internal combustion engine, such as agasoline engine or a diesel engine, and motors to which electric poweris supplied from a secondary battery capable of charging anddischarging, as power sources.

The hybrid vehicle has a battery unit 40, a vehicular drive unit 20, andan engine (not shown). The vehicular drive unit 20 has motor-generatorsMG1, MG2, a power split device 26 that distributes power among theengine (not shown) and the motor-generators MG1, MG2, and a powercontrol unit 21 that controls the motor-generators MG1, MG2.

The motor-generator MG1 mainly functions as a generator, and is operableto generate electric power using the output of the engine. Themotor-generator MG1 also operates as a starter when the engine isstarted. The motor-generator MG2 mainly functions as a motor, and isoperable to boost the output of the engine so as to increase the drivingforce. Also, the motor-generator MG2 generates electric power duringregenerative braking, so as to charge a battery B.

The battery unit 40 is provided with terminals 41, 42. The PCU 21 isprovided with DC terminals 43, 44. The terminal 41 and the DC terminal43 are electrically connected to each other by a cable 6, and theterminal 42 and the DC terminal 44 are electrically connected to eachother by a cable 8.

The battery unit 40 has the battery B, a system main relay SMR2connected between the positive electrode of the battery B and theterminal 41, a system main relay SMR3 connected between the negativeelectrode of the battery B and the terminal 42, and a system main relaySMR1 and a load-limiting resistor R which are connected in seriesbetween the positive electrode of the battery 13 and the terminal 41.The conduction/non-conduction states of the system main relays SMR1-SMR3are controlled according to a control signal SE supplied from a controldevice 30 which will be described later.

The battery unit 40 has a voltage sensor 10 that measures the voltage VBbetween the terminals of the battery B, and a current sensor 11 thatdetects the current IB that passes through the battery B. As the batteryB, a secondary battery, such as a nickel-metal hydride (NiMH) battery ora lithium-ion battery, a fuel cell, or the like, may be used. Acapacitor, such as an electric double layer capacitor, having a largecapacity may be used as an electric storage device, in place of thebattery B.

The power control unit 21 has inverters 22, 14 corresponding to themotor-generators MG1, MG2, respectively, a step-up converter 12 providedin common for the inverters 22, 14, and the control device 30.

The step-up converter 12 boosts the voltage between the DC terminals 43,44. The step-up converter 12 has a reactor 32 connected at one end tothe terminal 43, a boosting IPM (Intelligent Power Module) 13, and asmoothing capacitor 33. The boosting IPM 13 has IGBTs Q1, Q2 connectedin series between the output terminals of the step-up converter 12 thatgenerates a voltage VH after boosting, and diodes D1, D2 each of whichis connected in parallel with a corresponding one of the IGBTs Q1, Q2.The smoothing capacitor 33 smoothes the voltage boosted by the step-upconverter 12.

The other end of the reactor 32 is connected to an emitter of the IGBTQ1 and a collector of the IGBT Q2. The cathode of the diode D1 isconnected to a collector of the IGBT Q1, and the anode of the diode D1is connected to the emitter of the IGBT Q1. The cathode of the diode D2is connected to the collector, of the IGBT Q2, and the anode of thediode D2 is connected to an emitter of the IGBT Q2.

The inverter 14 converts the dc voltage generated by the step-upconverter 12 into three-phase alternating current, and delivers thecurrent to the motor-generator MG2 for driving the wheels. The inverter14 returns electric power generated by the motor-generator MG2 to thestep-up converter 12 during regenerative braking. At this time, thestep-up converter 12 is controlled by the control device 30 so as tooperate as a step-down circuit.

The inverter 14 has a U-phase arm 15, a V-phase arm 16, and a W-phasearm 17, which constitute an IPM 18 for running the vehicle. The U-phasearm 15, V-phase arm 16, and W-phase arm 17 are connected in parallelbetween the output lines of the step-up converter 12.

The U-phase arm 15 has IGBTs Q3, Q4 connected in series, and diodes D3,D4 connected in parallel with the IGBTs Q3, Q4, respectively. Thecathode of the diode D3 is connected to a collector of the IGBT Q3, andthe anode of the diode D3 is connected to an emitter of the IGBT Q3. Thecathode of the diode D4 is connected to a collector of the IGBT Q4, andthe anode of the diode D4 is connected to an emitter of the IGBT Q4.

The V-phase arm 16 has IGBTs Q5, Q6 connected in series, and diodes D5,D6 connected in parallel with the IGBTs Q5, Q6, respectively. Thecathode of the diode D5 is connected to a collector of the IGBT Q5, andthe anode of the diode D5 is connected to an emitter of the IGBT Q5. Thecathode of the diode D6 is connected to a collector of the IGBT Q6, andthe anode of the diode D6 is connected to an emitter of the IGBT Q6.

The W-phase arm 17 has IGBTs Q7, Q8 connected in series, and diodes D7,D8 connected in parallel with the IGBTs Q7, Q8, respectively. Thecathode of the diode D7 is connected to a collector of the IGBT Q7, andthe anode of the diode D7 is connected to an emitter of the IGBT Q7. Thecathode of the diode D8 is connected to a collector of the IGBT Q8, andthe anode of the diode D8 is connected to an emitter of the IGBT Q8.

An intermediate point of each phase arm is connected to a correspondingphase end of a corresponding phase coil of the motor-generator MG2:Namely, the motor-generator MG2 is a three-phase permanent-magnetsynchronous motor, and each of the three coils of U, V and W phases isconnected at one end to a neutral point. The other end of the U-phasecoil is connected to a node of the IGBTs Q3, Q4. The other end of theV-phase coil is connected to a node of the IGBTs Q5, Q6. The other endof the W-phase coil is connected to a node of the IGBTs Q7, Q8.

The current sensor 25 detects current passing through themotor-generator MG1 as a motor current value MCRT1, and outputs themotor current value MCRT1 to the control device 30. The current sensor24 detects current passing through the motor-generator MG2 as a motorcurrent value MCRT2, and outputs the motor current value MCRT2 to thecontrol device 30.

The inverter 22 and the inverter 14 are connected in parallel with eachother, to the step-up converter 12. The inverter 22 converts the dcvoltage generated by the step-up converter 12 into three-phasealternating current, and delivers the current to the motor-generatorMG1. The inverter 22 receives the voltage boosted by the step-upconverter 12, and drives the motor-generator MG1 in order to start theengine, for example.

Also, the inverter 22 returns electric power generated by themotor-generator MG 1 using torque transmitted from the crankshaft of theengine, to the step-up converter 12. At this time, the step-up converter12 is controlled by the control device 30 so as to operate as astep-down circuit. The internal arrangement of the inverter 22 issubstantially identical with that of the inverter 14, and thus will notbe described in detail.

The control device 30 receives torque command values TRI, TR2,respective values of motor speeds MRN1, MRN2, voltages VB, VL, VH, andcurrent IB, motor current values MCRT1, MCRT2, and a starting orignition signal IGON.

In this connection, the torque command value TR1, motor speed MRN1 andmotor current value MCRT1 are associated with the motor-generator MG1,and the torque command value TR2, motor speed MRN2 and motor currentvalue MCRT2 are associated with the motor-generator MG2. The voltage VBis a voltage applied to the battery B, and the current IB is a currentpassing through the battery B. The voltage VL is a voltage measuredbefore boosting of the step-up converter 12, and the voltage VH is avoltage measured after boosting of the step-up converter 12.

The control device 30 generates a control signal PWU as a command toboost the voltage, a control signal PWD as a command to step down thevoltage, and a signal CSDN as a command to inhibit operation, to thestep-up converter 12.

The control device 30 generates a drive command PWMI2 to convert the dcvoltage as the output of the step-up converter 12 into an ac voltage fordriving the motor-generator MG2, and a regeneration command PWMC2 toconvert the ac voltage developed by the motor-generator MG2 into a dcvoltage and return the dc voltage to the step-up converter 12, to theinverter 14. The control device 30 generates a drive command PWMI1 toconvert the dc voltage into an ac voltage for driving themotor-generator MG1, and a regeneration command PWMC1 to convert the acvoltage developed by the motor-generator MGI into a dc voltage andreturn the dc voltage to the step-up converter 12, to the inverter 22.

Next, the overall structure of the cooler for the power control unit 21will be described. FIG. 2 is a side elevation view showing the coolerfor the power control unit, in which the cooling fin structure accordingto this embodiment of the invention is used. FIG. 3 is a cross-sectionalview showing a planar configuration of the cooler for the power controlunit shown in FIG. 2.

Referring to FIG. 2 and FIG. 3, a plurality of semiconductor devices 62to be cooled are mounted on the cooler 60 for the power control unit.The semiconductor devices 62 constitute the IPM 18 (U-phase arm 15,V-phase arm 16 and W-phase arm 17) for running the vehicle, included ineach of the inverters 22, 14 shown in FIG. 1, and the boosting IPM 13 ofthe step-up converter 12. The semiconductor devices 62 generate heat asthe power control unit is driven.

The cooler 60 for the power control unit has an insulating plate 64, achannel top plate 66, a channel bottom plate 68, channel side walls 69,and a plurality of pin fins 71.

The insulating plate 64 is formed of a material having a high electricalinsulation property and high thermal conductivity. The insulating plate64 is formed of a ceramic material. In this embodiment, the insulatingplate 64 is formed of aluminum nitride (AIN). The above-indicatedplurality of semiconductor devices 62 are joined onto a surface of theinsulating plate 64 while being spaced from each other.

The channel top plate 66, channel bottom plate 68, channel side walls 69and pin fins 71 are formed of a material having high thermalconductivity. In this embodiment, the channel top plate 66, channelbottom plate 68, channel side walls 69 and pin fins 71 are formed ofaluminum. The channel top plate 66, channel bottom plate 68, channelside walls 69 and pin fins 71 constitute a heat sink that dissipatesheat generated at the semiconductor devices 62, to cooling water (LLC:long life coolant) as a coolant.

As a method of producing the cooler 60, the pin fins 71 may be formedintegrally with the channel top plate 66 or the channel bottom plate 68by die casting with an aluminum die, or the pin fins 71 may be formedsingly, and then mounted onto the channel top plate 66 and the channelbottom plate 68.

The channel top plate 66, channel bottom plate 68 and the channel sidewalls 69 are assembled together from four sides, to form a cooling waterpassage 80 through which the cooling water flows. The insulating plate64 to which the semiconductor devices 62 are joined is joined to thechannel top plate 66. The pin fins 71 are disposed in the cooling waterpassage 80. The pin fins 71 are shaped like pins that extend like rods,and are held upright between the channel top plate 66 and the channelbottom plate 68 such that the pin fins 71 are spaced apart from eachother.

The semiconductor devices 62 generate heat as the power control unit isdriven. The heat generated by the semiconductor devices 62 istransmitted to the pin fins 71 via the insulating plate 64 and thechannel top plate 66. On the other hand, the cooling water is suppliedfrom an electric pump (not shown) to the cooling water passage 80, andflows in one direction as indicated by arrows in FIG. 2 and FIG. 3. Inthe meantime, heat exchange takes place between the cooling water andthe pin fins 71, so that the heat generated by the semiconductor devices62 is dissipated.

In FIG. 3, the X-axis direction denotes a direction in which the coolingwater flows in the cooling water passage 80, and the Y-axis directiondenotes a direction orthogonal to the direction of flow of the coolingwater. The pin fins 71 extend in a direction orthogonal to the X-axisdirection and the Y-axis direction, between the channel top plate 66 andthe channel bottom plate 68.

The pin fins 71 are arranged in a zigzag form in the cooling waterpassage 80. Namely, a plurality of pin fins 71 arranged in a line (on acenterline 110A in FIG. 3) in the X-axis direction, and a plurality ofpin fins 71 located adjacent to the above-indicated plurality of pinfins 71 and arranged in a line (on a centerline 1108 in FIG. 3) in theX-axis direction are shifted from each other in the Y-axis direction. Inthe following description, the centerline 110A and the centerline 110Bwill be referred to as “centerline 110” when they are not distinguishedfrom each other.

Where a pin fin 71A as one of the pin fins 71 on the centerline 110A,and a pin fin 71B as one of the pin fins 71 on the centerline 110B,which is located adjacent to the pin fin 71A in an oblique direction(between the X-axis direction and the Y-axis direction) relative to thedirection of flow of the cooling water are focused on in FIG. 3, the pinfin 71A and the pin fin 71B are arranged at a pitch of Px as measured inthe X-axis direction, and are arranged at a pitch of Py as measured inthe Y-axis direction.

In this embodiment, the plurality of pin fins 71 are arranged so as tosatisfy a relationship that Px>Py. Furthermore, in this embodiment, thesize of the pitch Py is set so that a part of the pin fin 71A lies onthe pin fin 71B (i.e., the pin fin 71A overlaps the pin fin 71B) whenthe pin fin 71A is shifted in the X-axis direction toward the pin fin71B.

Next, the configuration of the pin fins 71 used in the cooler 60 for thepower control unit as shown in FIG. 2 and FIG. 3 will be described indetail. FIG. 4 is a cross-sectional view showing in enlargement a partof the cooler for the power control unit shown in FIG. 3.

Referring to FIG. 4, each of the pin fins 71 has an irregular, circularcross-section when it is cut in a plane containing the X-axis and theY-axis (which will be called “X-Y plane”). More specifically, the pinfin 71, when cut in the X-Y plane, has a cross-sectional shapeconsisting of a circular portion 72, and a curved portion 73 p and acurved portion 73 q (which will be referred to as “curved portion 73”when they are not particularly distinguished from each other).

The circular portion 72 has a circular shape. The circular portion 72has a radius R as measured from a center point 101 as a center of thecircle. The pitches Px, Py of the pin fins 71 located adjacent to eachother in an oblique direction relative to the direction of flow of thecooling water are determined with reference to the center points 101 ofthe circular portions 72 of the pin fins 71. The circular portion 72 hasouter peripheral surfaces 74 that contact the cooling water flowingthrough the cooling water passage 80. The outer peripheral surfaces 74are shaped along the circumference of a circle having a center at thecenter point 101 and the radius R.

The curved portions 73 are provided contiguously on the upstream sideand downstream side of the circular portion 72 as viewed in thedirection of flow of the cooling water. More specifically, the curvedportion 73 p is provided contiguously on the upstream side of thecircular portion 72 in the direction of flow of the cooling water, andthe curved portion 73 q is provided contiguously on the downstream sideof the circular portion 72 in the direction of flow of the coolingwater. The curved portion 73 p and the curved portion 73 q are symmetricwith respect to the center point 101 of the circular portion 72. Thecurved portion 73 p and the curved portion 73 q are separated from eachother by the circular portion 72 when viewed in the direction of flow ofthe cooling water.

The curved portion 73 p has an upstream end point 76 located at theupstream end of the pin fin 71 as viewed in the direction of flow of thecooling water, and the curved portion 73 q has a downstream end point 77located at the downstream end of the pin fin 71 as viewed in thedirection of flow of the cooling water. The upstream end point 76 andthe downstream end point 77 are located on the centerline 110 thatpasses through the center point 101 in the direction of flow of thecooling water. The curved portion 73 p is pointed at the upstream endpoint 76, and the curved portion 73 q is pointed at the downstream endpoint 77. The curved portion 73 p is tapered down toward the upstreamend point 76, such that the width B of the curved portion 73 p asmeasured in the Y-axis direction increases as a distance from theupstream end point 76 as measured in the X-axis direction increases. Thecurved portion 73 q is tapered down toward the downstream end point 77,such that the width B of the curved portion 73 q as measured in theY-axis direction increases as a distance from the downstream end point77 as measured in the X-axis direction increases.

While the curved portions 73 are pointed at the upstream end point 76and the downstream end point 77 in the above-described embodiment, theupstream end point 76 and the downstream end point 77 may be roundedwith a small radius, for some reason in terms of the production processfor forming the pin fins 71 using a die.

The curved portions 73 have curved faces 75 that contact the coolingwater flowing through the coaling water passage 80. More specifically,the curved faces 75 of the curved portions 73 of each pin fin 71 arelocated at respective positions that are opposed to four pin fins 71located adjacent to the pin fin 71 having the curved portions 73 inoblique directions relative to the direction of flow of the coolingwater.

The curved faces 75 of the curved portion 73 p extend from the upstreamend point 76 toward the downstream side in the direction of flow of thecooling water, on the opposite sides of the centerline 110, such thatthe curved faces 75 are contiguous with the outer peripheral surfaces 74of the circular portion 72. The curved faces 75 of the curved portion 73q extend from the downstream end point 77 toward the upstream side inthe direction of flow of the cooling water, on the opposite sides of thecenterline 110, such that the curved faces 75 are contiguous with theouter peripheral surfaces 74 of the circular portion 72. The curvedfaces 75 intersect with each other at the upstream end point 76 or thedownstream end point 77 so as to form a corner portion. In thisembodiment, the curved faces 75 intersect with each other at theupstream end point 76 or the downstream end point 77 so as to form anacute angle therebetween. The curved face 75 is continuously curvedbetween the upstream end point 76 or the downstream end point 77, and aposition at which the curved face 75 continues into the correspondingouter peripheral surface 74 of the circular portion 72. The curved face75 smoothly continues into the outer peripheral surface 74 of thecircular portion 72 while being curved. The curved faces 75 of thecurved portion 73 p and the curved faces 75 of the curved portion 73 qare formed so that the curved faces 75 of one of the curved portions 73p, 73 q are superimposed on those of the other of the curved portions 73p, 73 q when the above-indicated one of the curved portions 73 p, 73 qis rotated 180° about the center paint 101 of the circular portion 72.The curved faces 75 of each of the curved portions 73 p, 73 q aresymmetric with respect to the centerline 110.

Each of the curved faces 75 is curved in a concave shape as viewed fromthe center point 101 of the corresponding circular portion 72. In otherwords, the curved face 75 has a curved shape that is concaved toward thecenter point 101 of the circular portion 72. The curved face 75 iscurved to be recessed in a direction opposite to that of the outerperipheral surface 74 of the circular portion 72, as viewed from thecenter point 101 of the circular portion 72. The curved face 75 iscurved so that the absolute value of the slope of the curved face 75 inthe X-Y plane gradually increases as a distance from the upstream endpoint 76 or the downstream end point 77 as measured in the X-axisdirection increases. The curved face 75 is curved so that the rate ofincrease of the width B of the curved portion 73 gradually increases asthe distance from the upstream end point 76 or the downstream end point77 as measured in the X-axis direction increases.

Referring to FIG. 3 and FIG. 4, in the cooler 60 for the power controlunit in which the pin fins 71 are arranged in a zigzag form, adjacentrows of pin fins 71 arranged to be shifted from each other in thedirection orthogonal to the direction of flow of the cooling waterappear alternately, in the direction of flow of the cooling water.Therefore, the cooling water flows through the cooling water passage 80while detouring around the pin fins 71 that appear, ahead, andconsequently proceeds while winding on the opposite sides of thecenterline 110, as indicated by arrow 100 in FIG. 3. In this case, thecooling water repeatedly collides with the pin fins 71 while flowingthrough the cooling water passage 80, thus giving rise to a concernabout an increase in a pressure loss in the flow of the cooling water.

On the other hand, in the cooling fin structure of this embodiment, eachof. the pin fins 71 has an irregular, circular cross-section having thecircular portion 72 and the curved portions 73. With this configuration,the cooling water passage 80 having side walls provided by the outerperipheral surface 74 and curved face 75 of the pin fin 71A and theouter peripheral surface 74 and curved face 75 of the pin fin 71B isformed between the pin fin 71A and the pin fin 71B located in an obliquedirection relative to the direction of flow of the cooling water. Inthis embodiment in which the curved face 75 is curved in a concave shapeas viewed from the center point 101 of the circular portion 72, thecooling water passage 80 is shaped along a path of the cooling waterthat flows while detouring around the pin fins 71. With thisarrangement, the cooling water flows smoothly, and the pressure loss inthe cooling water passage 80 can be reduced.

Also, as compared with the case where each of the pin fins 71 consistssolely of the circular portion 72, the surface area of the pin fin 71that contacts the cooling water and the cross-sectional area of the pinfin 71 can be increased. Thus, the efficiency with which heat istransmitted from the pin fins 71 to the cooling water can be improved.

As an example of the cross-sectional shape of the pin fins used in thecooler, a streamline shape having a wing-like cross-section may beproposed. However, in this case, an upstream-side front end portion ofthe pin fin has a curved, arc-like surface; therefore, the cooling watercollides with the front end portion of the pin fin, and then changes itscourse in such a direction as to detour around the pin fin. It is thusdifficult to effectively reduce the pressure loss in the flow of thecooling water. On the other hand, in the cooling fin structure of thisembodiment in which the upstream end point 76 of the pin fin 71 has asharply pointed shape, the course of the cooling water can be smoothlychanged.

The plurality of pin fins 71 may also be located such that thedownstream end point 77 of the pin fin 71A located on the upstream sidein the flow of the cooling water is positioned downstream of theupstream end point 76 of the pin fin 71B located on the downstream side,as viewed in the direction of flow of the cooling water. In this case,the pressure loss in the flow of the cooling water in the cooling waterpassage 80 can be more effectively reduced, and the efficiency withwhich heat is transmitted from the pin fins 71 to the cooling water canbe more effectively improved.

Referring to FIG. 4, the configuration of the pin fins 71 will befurther described. In this embodiment, the curved faces 75 are shapedalong a circumference 130. More specifically, where the pin fin 71A andthe pin fin 71B located in oblique directions relative to each otherwith respect to the direction of flow of the cooling water are focusedon, one of the curved faced 75 of the pin fin 71A is shaped along thecircumference 130 having a center at the center point 101 of thecircular portion 72 of the pin fin 71B. Similarly, the remaining curvedfaces 75 of the pin fin 71A are shaped along circumferences drawn usingthe circular portions 72 of the other three pin fins 71 locatedobliquely from the pin fin 71 A relative to the direction of flow of thecooling water.

In the cooler using the pin fins, the heat-transfer performance isenhanced as a clearance or pitch between the pin fins is reduced. On theother hand, if the clearance or pitch between the pin fins isexcessively reduced, in an actual product, a foreign matter may be stuckor caught in between the pin fins, and may cause clogging of the coolingwater passage. Thus, in the cooling fin structure, of this embodiment,the size of the clearance between the pin fins 71 located adjacent toeach other in the Y-axis direction is set to a critical limit CL. Thecritical limit CL is determined in view of the type of the coolant, thevelocity of flow of the coolant, the capability of a filter for trappingforeign matters, etc., in an attempt to prevent clogging of the coolantpassage. As one example, the critical limit CL is equal to or largerthan 0.5 mm.

In this case, the pitch Px in the X-axis direction of the pin fin 71Aand the pin fin 71B located in oblique directions relative to each otherwith respect to the direction of flow of the cooling water is set to3^(1/2)(R+1/2×CL), and the pitch Py in the Y-axis direction of the pinfin 71A and the pin fin 71B is set to R+1/2×CL, while the radius of thecircumference 130 is set to R+CL.

With the above configuration, the cooling water flows smoothly betweenthe pin fins 71, and vortex is less likely or unlikely to be generatedaround the downstream end points 77 of the pin fins 71. Thus, thepressure loss in the flow of the cooling water in the cooling waterpassage 80 can be effectively reduced.

Also, in this embodiment, the pitch L between the center points 101 ofthe pin fin 71A and the pin fin 71B is set to 2R+CL. In this case, thewidth of the cooling water passage 80 formed between the pin fin 71A andthe pin fin 7113 is equal to CL. It is thus possible to increase thesurface area of the pin fins 71 that contact the cooling water, to themaximum, while keeping the width of the cooling water passage 80 at thecritical limit CL determined in view of clogging of the coolant passage.

FIG. 5 is a graph comparing the equivalent coefficient of heat transferfrom the pin fins to the cooling water in the cooling fin structure ofthis embodiment of the invention, with that of a cooling fin structureof a comparative example. FIG. 6 is a graph comparing a pressure loss inthe flow of the cooling water in the cooling fin structure of thisembodiment of the invention, with that of the cooling fin structure ofthe comparative example.

Referring to FIG. 5 and FIG. 6, the pin fins of the embodiment of theinvention have the same configuration and arrangement as the pin fins 71shown in FIG. 3 and FIG. 4 as described above. The pin fins in thecomparative example are columnar pin fins each of which consists solelyof the circular portion 72 (having the radius of R) of the pin fin 71 asshown in FIG. 4. When the equivalent coefficient of heat transfer fromthe pin fins to the cooling, water and the pressure loss in the flow ofthe cooling water were evaluated through a CAE analysis, the equivalentheat transfer coefficient obtained in the embodiment was higher by about1000 W/m²K than that of the comparative example, and the pressure lossobtained in the embodiment was lower by about 1000 kPa than that of thecomparative example.

The construction of the cooling fin structure according to theillustrated embodiment of the invention will be summarized as follows.The cooling fin structure of this embodiment is used in the cooler 60for the power control unit as an electronic device. The cooling finstructure includes a plurality of pin fins 71 arranged in a zigzag formin the cooling water passage 80 as a coolant passage through whichcooling water as a coolant flows. Each of the pin fins 71 has a circularportion 72 having a circular cross-section; and curved portions 73 asirregularly shaped portions provided contiguously on the upstream sideand downstream side of the circular portion 72 as viewed in thedirection of flow of the cooling water. Each of the curved portions 73is formed with a curved face 75 as an outer peripheral surface that iscurved along a circumference 130 having a center at the center point 101of the circular portion 72 of the pin fin 71 (71B) located adjacent tothe pin fin 71 (71A) having the above-indicated curved portion 73, in anoblique direction relative to the direction of flow of the coolingwater.

The construction of the cooling fin structure according to anotheraspect of the invention will be described. The cooling fin structure ofthis embodiment is used in the cooler 60 for the power control unit asan electric device. The cooling fin structure includes a plurality ofpin fins 71 arranged in a zigzag form in the cooling water passage 80 asa coolant passage through which cooling water as a coolant flows. Eachof the pin fins 71 has a circular portion 72 having a circularcross-section, and curved portions 73 as irregularly shaped portionsprovided contiguously on the upstream side and downstream side of thecircular portion 72 as viewed in the direction of flow of the coolingwater. Each of the curved portions 73 is formed with curved faces 75 asouter peripheral surfaces, which are curved into a concave shape asviewed from the center point 101 of the circular portion 72, on theopposite sides of the centerline 110 as a straight line that extendsfrom the center point 101 of the circular portion 72 in the direction offlow of the cooling water.

With the cooling fin structure constructed as described above accordingto the embodiment of the invention, it is possible to reduce thepressure loss in the flow of the cooling water in the cooling waterpassage 80, while improving the efficiency with which heat istransferred from the pin fins 71 to the cooling water, in the cooler 60for the power control unit including the pin fins 71 arranged in azigzag form. Consequently, the semiconductor devices 62 that constitutethe power control unit are cooled with improved efficiency.

The present invention may also be applied to coolers for power controlunits installed on, for example, a fuel cell hybrid vehicle (FCHV) usinga fuel cell and a secondary battery as power sources, and an electricvehicle (EV). While the internal combustion engine is driven at anoperating point at which the fuel efficiency is optimized in the hybridvehicle of the illustrated embodiment, the fuel cell is driven at anoperating point at which the power generation efficiency is optimized inthe fuel cell hybrid vehicle. Also, there is basically no difference inconnection with the use of the secondary battery, between the fuel cellhybrid vehicle and the hybrid vehicle of the illustrated embodiment.

While the invention has been described with reference to an exemplaryembodiment thereof, it is to be understood that the invention is notlimited to the described exemplary embodiment or construction. To thecontrary, the invention is intended to cover various modifications andequivalent arrangements. In addition, while the various elements of theexemplary embodiment are shown in various combinations andconfigurations, other combinations and configurations, including more,less or only a single element, are also within the scope of theinvention.

This invention is mainly applied to a cooler for cooling a heatgenerator, such as a semiconductor device.

1. A cooling fin structure used in a cooler for an electric device,comprising a plurality of pin fins arranged in a zigzag form in acoolant passage through which a coolant flows, wherein: each of the pinfins has a circular portion having a circular cross-section, and curvedportions provided contiguously on the upstream side and downstream sideof the circular portion as viewed in a direction of flow of the coolant;the curved portions have an outer peripheral surface that is formedalong a circumference having a center at a center point of the circularportion of an adjacent one of the pin fins that is located adjacent tothe pin fin having the curved portions, in an oblique direction relativeto the direction of flow of the coolant; and each of the curved portionshas opposite curved faces formed contiguously with outer peripheralsurfaces of the circular portion and each of the opposite curved facesis provided by the outer peripheral surface formed along thecircumference.
 2. The cooling fin structure according to claim 1,wherein when a first pitch between the pin fins located adjacent to eachother in an oblique direction relative to the direction of flow of thecoolant, as measured in a direction orthogonal to the direction of flowof the coolant, is equal to R+1/2×CL, and a second pitch between the pinfins located adjacent to each other in the oblique direction, asmeasured in the direction of flow of the coolant, is equal to3^(1/2)(R+1/2×CL), where R is a radius of the circular portion, and CLis a clearance between the pin fins located adjacent to each other inthe direction orthogonal to the direction of flow of the coolant, theouter peripheral surface is shaped along the circumference having aradius of R+CL.
 3. The cooling fin structure according to claim 1,wherein the opposite curved faces are formed on opposite sides of acenterline that passes through the center point of the circular portion.4. The cooling fin structure according to claim 1, wherein: the curvedportions of each of the pin fins include an upstream end point locatedat an upstream end of the pin fin having the curved portions, as viewedin the direction of flow of the coolant, and a downstream end pointlocated at a downstream end of the pin fin as viewed in the direction offlow of the coolant; and the pin fins located adjacent to each other inan oblique direction relative to the direction of flow of the coolantare positioned such that the downstream end point of the curved portionsof the pin fin located on the upstream side is located downstream of theupstream end point of the curved portions of the pin fin located on thedownstream side, as viewed in the direction of flow of the coolant. 5.The cooling fin structure according to claim 1, wherein the curvedportion located on the upstream side of the circular portion and thecurved portion located on the downstream side of the circular portionare symmetric with respect to the center point of the circular portion.6. A cooling fin structure used in a cooler for an electric device,comprising a plurality of pin fins arranged in a zigzag form in acoolant passage through which a coolant flows, wherein: each of the pinfins has a circular portion having a circular cross-section, and curvedportions provided contiguously on the upstream side and downstream sideof the circular portion as viewed in a direction of flow of the coolant;and each of the curved portions is formed with outer peripheral surfacesthat are curved into a concave shape as viewed from a center point ofthe circular portion, at opposite sides of a straight line that passesthrough the center point of the circular portion in the direction offlow of the coolant.
 7. The cooling fin structure according to claim 6,wherein: the curved portions of each of the pin fins include an upstreamend point located at an upstream end of the pin fin having the curvedportions, as viewed in the direction of flow of the coolant, and adownstream end point located at a downstream end of the pin fin asviewed in the direction of flow of the coolant; and the pin fins locatedadjacent to each other in an oblique direction relative to the directionof flow of the coolant are positioned such that the downstream end pointof the curved portions of the pin fin located on the upstream side islocated downstream of the upstream end point of the curved portions ofthe pin fin located on the downstream side, as viewed in the directionof flow of the coolant.
 8. The cooling fin structure according to claim6, wherein the curved portion located on the upstream side of thecircular portion and the curved portion located on the downstream sideof the circular portion are symmetric with respect to the center pointof the circular portion.
 9. The cooling fin structure according to claim6, wherein: the curved portions of each of the pin fins include anupstream end point located at an upstream end of the pin fin having thecurved portions, as viewed in the direction of flow of the coolant, anda downstream end point located at a downstream end of the pin fin asviewed in the direction of flow of the coolant; and the outer peripheralsurfaces of each of the curved portions intersect with each other at anacute angle at the upstream end point and the downstream end point.